1. Field of the Art
The present invention relates to a contact lens cleaning solution and a method of cleaning a contact lens using the solution.
2. Discussion of the Related Art
As conventionally used non-water-absorbable contact lenses, there are known a hard contact lens of polymer made mainly of methyl methacrylate, a high-degree oxygen permeable hard contact lens of polymer made mainly of siloxanyl methacrylate, fluoroalkyl methacrylate, or the like, and a non-water-absorbable soft contact lens made mainly of a silicone rubber that contains polydimethylsiloxane as a major component, or a butyl rubber that contains butyl acrylate as a major component. The surfaces of these non-water-absorbable contact lenses are hydrophobic. In particular, the surfaces of the high-degree oxygen permeable contact lens which has recently attracted public attention exhibit a high degree of hydrophobic property. The hydrophobic property of the lens surfaces causes a problem that lipid deposits which derive from tear fluid and lipid of the eyes adhere to the lens surfaces when the non-water-absorbable contact lenses are worn on the eyes of a user, whereby the contact lens is clouded, leading to deteriorated eyesight of the lens user.
In an attempt to deal with the above-described problem, there are proposed various methods of rendering the hydrophobic surfaces of the contact lens hydrophilic. Examples of the proposed methods include a plasma surface treatment and a chemical treatment using an acid or an alkali. However, the contact lens treated by these methods does not exhibit satisfactory durability in its hydrophilic property at the surfaces thereof, and it is considerably cumbersome to repeat the treatment for rendering the lens surfaces hydrophilic. Thus, the proposed methods are not practical.
Further, there is known a method which uses a so-called wetting solution so as to improve the surfaces of the contact lens. In this method, the contact lens is immersed in a solution that contains a hydrophilic polymer, so that the polymer is fixed to the surfaces of the contact lens. This method permits the contact lens to be repeatedly subjected to the treatment for rendering the lens surfaces hydrophilic, by simply immersing the contact lens in the solution as needed. Thus, the hydrophilic property of the contact lens surfaces is comparatively easily maintained. For instance, JP-B-48-37910 discloses a solution for a contact lens containing polyvinyl alcohol and a water-soluble polymer such as hydroxyethyl cellulose and polyvinyl pyrrolidone.
Such a treatment solution is effective for a contact lens having a comparatively low degree of hydrophobic property, such as a high-degree oxygen permeable contact lens of polymer made mainly of methyl methacrylate. However, the solution is not effective for a contact lens having a high degree of hydrophobic property, such as a non-water-absorbable contact lens which contains a large amount of a silicone or fluorine component, since the water-soluble polymer included in the solution is not likely to adhere to the surfaces of the contact lens. Thus, the solution as described above is not capable of effectively rendering the surfaces of the contact lens hydrophilic.
JP-A-63-246718 discloses a surface treatment solution for a contact lens which consists of a polymeric material with an ionic charge. In effecting the treatment for rendering the surfaces of the contact lens hydrophilic by using the disclosed surface treatment solution, the surfaces of the contact lens need to have an ionic charge opposite to that of the solution. Further, the density of the opposite ionic charge of the lens surfaces needs to be higher than a certain level. For satisfying these requirements, it is necessary to effect a treatment for increasing the density of the ionic charge of the contact lens surfaces, prior to the treatment for rendering the lens surfaces hydrophilic, undesirably making the procedure cumbersome. Like the wetting solution as described above, the disclosed polymeric solution which contains the ionic group that gives the ionic charge as described above is not capable of giving a satisfactory degree of hydrophilic property to the non-water-absorbable contact lens which contains a large amount of the silicone or fluorine component.
JP-A-3-235914 discloses various contact lens solutions which contain gum arabic as a hydrophilicity rendering component. The gum arabic contained in the contact lens solutions is effectively adsorbed on the highly hydrophobic surfaces of the contact lens. Accordingly, the solutions disclosed in the publication are effective to give the hydrophilic property to the non-water-absorbable contact lens which contains a large amount of silicone or fluorine component. The contact lens whose surfaces are rendered hydrophilic by using these solutions assures the lens user of its comfortable wearing.
While the contact lenses are worn on the eyes, protein included in the tear fluid adheres or clings to the surfaces of the contact lenses. In view of this, there have been conventionally proposed various methods of cleaning and removing protein deposits adhering to the contact lenses by using a cleaning agent that contains a protease, for instance. JP-A-2-168224 and JP-A-6-9504 disclose methods of removing such protein deposits by decomposition using the protease.
The treatment for rendering the lens surfaces hydrophilic by the gum arabic and the treatment for removing the protein deposits by the protease are both necessary for the contact lenses to be worn on the eyes of the user. It would be considerably convenient to the user if the user can effect these treatments simultaneously in one step, rather than in different steps. In other words, the surfaces of the contact lens can be rendered hydrophilic while, at the same time, the protein adhering to the surfaces of the contact lens can be removed, in a single step of immersing the contact lens in a mixture of a solution containing the protease and a solution of the gum arabic which effectively gives the hydrophilic property to the contact lens.
However, a study by the inventors of the present invention revealed that such a contact lens solution containing the gum arabic and protease considerably deteriorates a cleaning effect to be exhibited by the protease, namely, an effect of the protease to remove the protein deposits by decomposition.